1. Field of the Invention
The present invention relates to a fuel gas feeding system for feeding a fuel gas to an internal combustion engine for burning a fuel gas such as a compressed natural gas.
2. Description of the Related Art
In recent years, a natural gas has been employed as one of alternate fuels for gasoline or gas oil. In the case in which the natural gas is to be used as a fuel of an internal combustion engine for vehicles, a fuel gas feeding system as described in JP-A-7-189731 is used, for example, in which a high pressure cylinder filled with a natural gas compressed to have a pressure of approximately 200 kg/cm2 is mounted on a vehicle and the natural gas is fed from the high pressure cylinder to a combustion chamber of the internal combustion engine through a fuel gas feeding passageway, a pressure regulator and a fuel injection valve.
In such a fuel gas feeding system, it is necessary to rapidly detect a situation in which a hole is formed in the fuel gas feeding passageway and a fuel leaks out, thereby taking a countermeasure in an early stage.
In view of this respect, it is an object of the invention to provide a fuel gas feeding system having a failure diagnosing function capable of rapidly detecting that a leakage is generated in the fuel gas feeding passageway for feeding a fuel gas to an internal combustion engine.
In order to achieve the object, a first aspect of the invention is directed to a fuel gas feeding system having a fuel gas feeding passageway (11, 12) for feeding a fuel gas to an internal combustion engine and a plurality of cutoff valves (24, 41, 7) provided in the middle of the fuel gas feeding passageway, the system comprising a pressure sensor (32, 33) for detecting a pressure in a portion partitioned by adjacent two of the cutoff valves in the fuel gas feeding passageway, an engine stop detecting unit detecting stop of the engine, and a failure detecting unit for closing the two adjacent cutoff valves when the stop of the engine is detected, measuring a reducing amount of a pressure detected by the pressure sensor after a predetermined decision time (T0, T2) passes, and deciding that a leakage is generated between the two adjacent cutoff valves when the reducing amount thus measured is equal to or larger than a predetermined reducing amount (xcex94P0, xcex94P2).
The xe2x80x9cpredetermined decision time (T0, T2)xe2x80x9d and the xe2x80x9cpredetermined reducing amount(xcex94P0, xcex94P2)xe2x80x9d are set according to a leakage amount (volume/time) per unit time to be decided as a failure and the volume of the passageway to be decided.
According to such a structure, the adjacent two of the cutoff valves provided in the middle of the fuel gas feeding passageway are closed. Consequently, the reducing amount of the pressure in the closed passageway is measured after the predetermined decision time passes. When the reducing amount thus measured is larger than the predetermined reducing amount, it is decided that a leakage is generated between the two adjacent cutoff valves. Therefore, in the case in which the leakage is generated in the fuel gas feeding passageway, it is possible to rapidly decide which portion partitioned by the cutoff valves provided in the passageway generates the leakage.
A second aspect of the invention is directed to the fuel gas feeding system according to the first aspect of the invention, wherein the fuel gas feeding passageway includes a high pressure passageway (11) partitioned by a first cutoff valve (24) and a second cutoff valve (41) and having a comparatively high pressure of a fuel gas and a low pressure passageway (12) partitioned by the second cutoff valve (41) and a third cutoff valve (7) and having a comparatively low pressure of the fuel gas, a pressure regulator (51, 61) is provided between the low pressure passageway (12) and the second cutoff valve (41), and the failure detecting unit sets the predetermined decision time (T2) required for deciding presence of a leakage in the low pressure passageway (12) depending on a pressure (P0) in the high pressure passageway and a temperature (TG2) of the fuel gas in the low pressure passageway.
According to such a structure, the predetermined decision time required for deciding presence of a leakage in the low pressure passageway is set depending on the pressure in the high pressure passageway and the temperature of the fuel gas in the low pressure passageway. It is considered that a reducing speed of the pressure in the low pressure passageway is reduced due to the leakage if the pressure in the high pressure passageway is high and the temperature of the fuel gas in the low pressure passageway is low. The predetermined decision time is set to be longer when the pressure in the high pressure passageway is increased and the temperature of the fuel gas in the low pressure passageway is dropped. Consequently, the decision can be carried out accurately.